Diastolic Heart Failure (“DHF”), a major cause of morbidity and mortality, is a clinical phenomena characterized by low cardiac output and/or symptoms of congestion with normal (or above normal) ejection fraction. Clinical diagnosis of DHF may typically also require evidence of reduced left ventricular (LV) filling. This evidence may be obtained from a Doppler echo examination, for example.
DHF may relate to a disease of the myocardium, or may alternately be indicative of other clinical pathologies such as hypertension, myocardial infarction, coronary artery disease, aging, diabetes mellitus, obesity, or aortic stenosis, for example without limitation. Hypertension may be an important co-morbidity of DHF, accounting for about 60% of patients with DHF. DHF may represent more than about 40% of the total congestive heart failure (“CHF”) population according to some estimates.
Appropriate clinical treatment for DHF is not as well established as for systolic heart failure (“SHF”), and usually mimics the treatment given for SHF, despite the fact that the underlying disease processes are not necessarily similar. A type of treatment may include pharmacologic treatment, such as calcium channel blockers, diuretics, inotropes, beta-blockers and ACE inhibitors, for example. Some evidence may suggest DHF patients may respond to cardiac resynchronization therapy (CRT), but evidence to support this hypothesis is currently lacking.
DHF patients often have thick, hypertrophic ventricular walls, resulting in increased myocardial “stiffness.” Increased sympathetic tone may lead to higher than normal basal heart rates in patients with DHF. However, DHF patients may not benefit from an increase in heart rate, and may experience a worsening of symptoms in some cases, since an increase in rate tends to reduce LV diastolic filling time, and hence, may further reduce LV filling. Increasing HR in a patient with DHF may also reduce coronary perfusion (which may depend on filling time). Symptoms that may arise due to DHF may become more pronounced during exercise, since end diastolic volume in a DHF patient tends to stay the same during exercise, rather than increasing to meet increased demands. Thus, tolerable ranges for heart rate for a patient with DHF may be more difficult to determine than for other individuals.